Light source, optical pickup, and electronic apparatus

ABSTRACT

A light source of the present invention includes: a semiconductor light emitting device which has a light emitting face and emits light from part of the light emitting face; a container which has a light transmitting window for transmitting the light and accommodates the semiconductor light emitting device; and a gettering portion for performing gettering of a material containing at least one of carbon and silicon. The gettering portion is positioned, in the container, in a region other than the part of the light emitting face of the semiconductor light emitting device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of copending U.S. application Ser. No.10/993,812 filed Nov. 19, 2004, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates generally to a light source provided witha semiconductor light emitting device. The light source is widely usedfor various kinds of electronic apparatuses such as an optical diskapparatus, a copy machine, a printer, a lighting apparatus, opticalcommunication application, and a laser display.

A semiconductor laser formed from a III-V group nitrogen semiconductormaterial (Al_(x)Ga_(y)In_(1-x-y)N (where 0≦x≦1, and 0≦y≦1)) is a keydevice for realizing ultra high density recording in an optical diskapparatus. Presently, as a light source required for data recording withhigher density than DVD, a GaN blue-violet semiconductor laser is theclosest one to the practical level. Increase in power of the blue-violetsemiconductor laser enables high-speed writing to an optical disk torealize, and additionally, the increase in power of the blue-violetsemiconductor laser is an essential technique for pioneering newtechnical fields such as an application to a laser display.

Hereinafter, with reference to FIGS. 7A and 7B, a prior-art blue-violetsemiconductor laser will be described. The semiconductor laser 801 shownin the figures includes a substrate 701 and a multilayer structureformed on the substrate 701. The multilayer structure includes, from theside of the substrate 701, an n-AlGaN cladding layer 702, a quantum wellactive layer 703, a p-AlGaN cladding layer 704, and a p-GaN contactlayer 705. In an upper portion of the semiconductor multilayerstructure, the p-AlGaN cladding layer 704 and part of the p-GaN contactlayer 705 are processed so as to have a stripe shape, so as to form aridge stripe 706 for current confinement. Both sides of the ridge stripe706 are covered with an insulating layer 707. A p-electrode 708 isformed on a top face of the ridge stripe 706, and an n-electrode 709 isformed on a back face of the substrate 701.

In the operation, according to an increase in current injected from thep-electrode 708 and the n-electrode 709, a carrier density in thequantum well active layer 703 is increased. When the value reaches apredetermined threshold carrier density, laser oscillation is obtained.

In a rewritable optical disk apparatus, a high-power semiconductor laseris desired. A conventional technique is used in which reflectivities oftwo end faces constituting a cavity (resonator) of a semiconductor laserare asymmetric for the purpose of realizing higher power.

In a semiconductor laser used for writing to an optical disk, cavity endfaces are coated with dielectric multilayer films, so thatreflectivities of the end faces are made to be asymmetric. One of thecavity end faces on the side from which laser light is emitted (a lightemitting end face) is made to have a lower reflectivity, and the endface on the other side (a back end face) is made to have a higherreflectivity. For example, the reflectivity of the light emitting endface is set to be 10%, and the reflectivity of the back end face is setto be 90%. The reflectivity of the dielectric multilayer film can becontrolled by a refractive index and a thickness of a dielectric layerto be deposited, and the number of layers to be stacked.

The semiconductor laser 801 shown in FIG. 7A is packaged in a canpackage (container) shown in FIG. 8A, and used as a light radiatingelement of short-wavelength light. The package (a short-wavelength lightsource) includes a base 803 and a cap 804. The semiconductor laser 801and a sub-mount 802 functioning as a radiator are mounted on the base803. The cap 804 includes a glass plate 806 functioning as a lighttransmitting window for taking out the light, and a metal foundation(can) 805. The semiconductor laser 801 is mounted on the base 803 viathe sub-mount 802. In the base 803, openings for terminals are disposed,and the terminals are fixedly attached by a low-melting glass 807.

In order to maintain the air-tightness in the package, a gap between theglass plate 806 and the can 805 is closed by a low-melting glass 808(fixed at several hundreds of degrees), as shown in FIG. 8B. An internalspace enclosed by the base 803 and the cap 804 is filled with a nitrogen(N₂) gas or the like.

However, the short-wavelength light source shown in FIG. 8A causes aproblem that when the semiconductor laser 801 operates with high opticaloutput power of about 30 mW for a long period of time, a foreignmaterial is elliptically deposited on the light emitting end face of thesemiconductor laser 801.

It is found by elemental analysis (mass spectrometry such as EDX) thatthe for eign material is a material mainly including carbon (C) orsilicon (Si). It is also found that the deposition of the foreignmaterial is increased in accordance with the increase in optical powerof the semiconductor laser 801. Therefore, the phenomenon of thedeposition of the foreign material is a serious problem for increasingthe power of the light source and for realizing high-speed recording toa rewritable optical disk apparatus.

According to experiments by the inventors of the present invention, itis also found that the deposition of foreign material is not only causedin the inside of the package shown in FIG. 8A. Specifically, in variouselectronic apparatuses (an optical pickup apparatus, for example)provided with a short-wavelength semiconductor laser with an oscillationwavelength of 450 nm or less, it is observed that the foreign materialis deposited on a portion irradiated with laser light (especially in aportion with higher optical density). On the contrary, since thephenomenon of the deposition of the foreign material is not observed inother semiconductor lasers (a red laser, or an infrared laser), it isconsidered that the phenomenon remarkably occurs in short-wavelengthsemiconductor lasers with oscillation wavelength of 450 nm or less. Inaddition, such a phenomenon may cause even in a visible range ofwavelengths when the optical power is increased.

The C and Si deposited in the package shown in FIG. 8A can be derivedfrom various materials of slight amounts existing in the air(hydrocarbon or siloxane). For this reason, it is extremely difficult toperform an assembly process in a condition where deposition causativematerials such as C or Si are not mixed in the package. In addition, itis impossible in reality to prevent the causative materials existing inthe air from entering the optical disk apparatus. Even if the inside ofthe package can be held in a condition of C-free or Si-free, it isimpossible to prevent the materials including C or Si from depositing onoptical components such as a lens which is irradiated withshort-wavelength laser light emitted from the light source.

SUMMARY OF THE INVENTION

The invention provides a light source capable of stably operating ashort-wavelength semiconductor laser or a high-power semiconductor laserfor the long term, an optical pickup, and an electronic apparatus.

The light source of the present invention includes: a semiconductorlight emitting device which has a light emitting face and emits lightfrom part of the light emitting face; a container which has a lighttransmitting window for transmitting the light and accommodates thesemiconductor light emitting device; and a gettering portion forperforming gettering of a material containing at least one of carbon andsilicon, wherein the gettering portion is positioned, in the container,in a region other than the part of the light emitting face of thesemiconductor light emitting device.

In a preferred embodiment, the semiconductor light emitting deviceincludes: a substrate; a multilayer structure including a firstconductive-type cladding layer, an active layer, and a secondconductive-type cladding layer, the multilayer structure being formed onthe substrate; a main current confinement structure for injecting acarrier into a first region of the active layer; and a sub currentconfinement structure for injecting a carrier into a second region ofthe active layer, and a portion of the light emitting face from whichlight generated in the second region of the active layer is emittedfunctions as the gettering portion.

In a preferred embodiment, the container includes: a supporting memberon which the semiconductor light emitting device is placed; and a cap towhich the light transmitting window is fixedly attached, the capcovering the semiconductor light emitting device, and the getteringportion is positioned on the supporting member.

In a preferred embodiment, the container includes: a supporting memberon which the semiconductor light emitting device is placed; and a cap towhich the light transmitting window is fixedly attached, the capcovering the semiconductor light emitting device, and the getteringportion is positioned in a region of an inner face of the lighttransmitting window which is not irradiated with the light.

In a preferred embodiment, the semiconductor light emitting device isformed from a III-V group nitride semiconductor material.

In a preferred embodiment, a TiO₂ layer is formed in part of a regionwhich is irradiated with the light in the container.

In a preferred embodiment, an oscillation wavelength of thesemiconductor light emitting device is λ, and a refractive index of theTiO₂ layer is n, a thickness of the TiO₂ layer is substantially anintegral multiple of λ/(2n).

The fabrication method of a light source according to the inventionincludes the steps of: preparing a semiconductor light emitting devicewhich has a light emitting face and emits light from part of the lightemitting face; preparing a container which has a light transmittingwindow for transmitting the light and accommodates the semiconductorlight emitting device; accommodating the semiconductor light emittingdevice in the container, thereby blocking the semiconductor lightemitting device from the air; and performing gettering of a materialcontaining at least one of carbon and silicon, by irradiating a regionof the light emitting face other than the part of the light emittingface of the semiconductor light emitting device with light in the insideof the container.

In a preferred embodiment, a wavelength of light with which theirradiation is performed in the gettering step is 450 nm or less.

In a preferred embodiment, the irradiation with light is performed byusing an Hg lamp, a blue LED, a blue laser, an ultraviolet LED, or anultraviolet laser.

In a preferred embodiment, the semiconductor light emitting device isformed from a III-V group nitride semiconductor material.

The optical unit according to the present invention includes: asemiconductor light emitting device which has a light emitting face andemits light from part of the light emitting face; a photo-detectionelement; a container which has a light transmitting window fortransmitting the light and accommodates the semiconductor light emittingdevice and the photo-detection element; and a gettering portion whichperforms gettering of a material containing at least one of carbon andsilicon, wherein the gettering portion is positioned in a region of thelight emitting face other than the part of the light emitting face ofthe semiconductor light emitting device in the inside of the container.

In a preferred embodiment, a wavelength of the light is 450 nm or less.

The optical pickup apparatus of the present invention includes: asemiconductor light emitting device which has a light emitting face andemits light from part of the light emitting face; an optical system forconverging the light emitted from the semiconductor light emittingdevice onto a recording medium; a photo detector for detecting lightreflected from the recording medium; and a gettering portion forperforming gettering of a material containing at least one of carbon andsilicon, wherein the gettering portion is positioned in a region of thelight emitting face other than the part of the light emitting face ofthe semiconductor light emitting device.

In a preferred embodiment, a wavelength of the light is 450 nm or less.

In a preferred embodiment, the optical pickup apparatus furtherincludes: a semiconductor substrate for supporting the semiconductorlight emitting device, wherein the photo detector includes a pluralityof photo diodes formed on the semiconductor substrate.

In a preferred embodiment, the semiconductor substrate is formed fromsilicon, the semiconductor substrate has a recessed portion formed on aprincipal surface and a micro mirror formed on one side face of therecessed portion, the semiconductor light emitting device is disposed inthe recessed portion of the silicon substrate, and an angle formed bythe micro mirror and the principal surface of the semiconductor lightemitting device is set so that the light emitted from the semiconductorlight emitting device travels in a direction substantially perpendicularto the principal surface by means of the micro mirror.

In a preferred embodiment, the semiconductor light emitting device isformed from a III-V group nitride semiconductor material.

The electronic apparatus of the present invention includes: asemiconductor light emitting device which has a light emitting face andemits light from part of the light emitting face; and an apparatus forperforming gettering, decomposition, or vaporization of a materialcontaining at least one of carbon and silicon.

In a preferred embodiment, the apparatus is an apparatus for generatingplasma.

In a preferred embodiment, the apparatus includes a light source whichemits light having a wavelength of 450 nm or less.

In a preferred embodiment, the electronic apparatus further comprises aphoto catalytic effect material film disposed in a position whichreceives at least part of the light emitted from the light source,wherein the photo catalytic effect material film has a function ofdecomposing and vaporizing a compound of carbon or Si.

In a preferred embodiment, the light source is an Hg lamp, a blue LED, ablue laser, an ultraviolet LED, or an ultraviolet laser.

In a preferred embodiment, the semiconductor light emitting device isformed from a III-V group nitride semiconductor material.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary as well as the following detailed description ofthe preferred embodiments of the invention, will be better understoodwhen read in conjunction with the appended drawings. For the purpose ofillustrating the invention, there is shown in the drawings an embodimentwhich is presently preferred. It should be understood, however, that theinvention is not limited to the precise arrangements andinstrumentalities shown.

FIG. 1 is a perspective view of a semiconductor laser used in a firstembodiment of a light source according to the present invention.

FIG. 2A is a section view showing a construction of a second embodimentof a light source of the present invention, FIG. 2B is a partiallyenlarged section view showing the vicinity of an adhesive portion of aglass and a can, and FIG. 2C is a partially enlarged section viewshowing the vicinity of an adhesive portion of a glass and a can inanother configuration.

FIG. 3A is a section view showing a construction of a third embodimentof a light source according to the present invention, and FIG. 3B is aview for illustrating a fabrication method thereof.

FIG. 4A is a perspective view of an optical unit used in an embodimentof an optical pickup apparatus according to the present invention, andFIG. 4B is a view showing a construction of an optical pickup in theembodiment.

FIG. 5 is a construction view of an embodiment of an electronicapparatus (an optical disk apparatus) according to the presentinvention.

FIG. 6 is a construction view showing another embodiment of anelectronic apparatus (an optical disk apparatus) according to thepresent invention.

FIG. 7A is a construction view of a prior-art semiconductor laser, andFIG. 7B is a view showing a position in which a foreign material isdeposited in the prior-art semiconductor laser.

FIG. 8A is a construction view of an example of a prior-artsemiconductor laser element, and FIG. 8B is a partially enlarged sectionview showing the vicinity of an adhesive portion of a glass and a can.

FIG. 9 is a view showing an embodiment of a laser projection-typedisplay.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

With reference to FIG. 1, a first embodiment of a light source accordingto the present invention will be described.

The light source of this embodiment comprises a nitride semiconductorlaser element accommodated in a container which is not shown. Thecontainer may have a known construction as shown in FIG. 8A, forexample. A main feature of this embodiment resides in that part of thesemiconductor laser element functions as a gettering portion forperforming gettering of a material containing at least one of carbon andsilicon.

The semiconductor laser in this embodiment includes an n-type GaNsubstrate 101 and a semiconductor multilayer structure formed on then-type GaN substrate 101, as shown in FIG. 1. The semiconductormultilayer structure includes an n-type cladding layer (a first claddinglayer) 102 of n-type AlGaN, a quantum well active layer 103 of a multiquantum well structure including InGaN, a p-type cladding layer (asecond cladding layer) 104 of p-type AlGaN, and a contact layer 105 ofp-type GaN.

The semiconductor laser includes a main stripe structure 106 a forinjecting carriers into a first region 103 a of the active layer 103 anda sub stripe structure 106 b for injecting carriers into a second region103 b of the active layer 103. In the semiconductor laser, a portion inwhich the main stripe structure 106 a is formed functions as a firstsemiconductor laser 201 which emits laser light in operation. On theother hand, in the semiconductor laser, a portion in which the substripe structure 106 b is formed functions as a second semiconductorlaser 202 which performs laser emission required for the gettering whenthe gettering is to be performed. Specifically, among the light emittingend faces of the shown semiconductor laser, a portion from which lightgenerated in the second region 103 b of the active layer 103(short-wavelength light having wavelengths of 450 nm or less, forexample) is emitted functions as the gettering portion 203. Depositionscontaining carbon or Si are formed on the portion and the peripherythereof.

The main stripe structure 106 a and the sub stripe structure 106 b inthis embodiment are both formed by processing the p-type contact layer105 and the p-type cladding layer (the second cladding layer) 104 so asto have ridge stripe shapes. In an upper face of the semiconductormultilayer structure, a p-electrode 108 is formed in the ridge portion,and an insulating layer 107 is formed in the other portion. On a backface of the n-GaN substrate 1, an n-electrode 109 is formed.

In this embodiment, a cavity length, a chip width, and a thickness ofthe semiconductor laser are set to be 600 μm, 400 μm, and 80 μm,respectively. A ridge stripe width of the first semiconductor laser 201is about 1.7 μm, and a ridge stripe width of the second semiconductorlaser 202 is 10 μm.

In the light source of this embodiment with the above-describedconfiguration, the second semiconductor laser 202 is used fordecomposing materials containing C and Si included in the atmosphere inthe container, and preferentially depositing (gettering) the decomposedmaterials on the emitting end face. Therefore, the second semiconductorlaser 202 operates and emits laser light, only when the gettering isrequired.

In the case where the above-described semiconductor laser is mounted ina package so as to block off the air of the outside, typically, thesemiconductor laser become commercially available after the gettering bythe second semiconductor laser 202 is performed. After the semiconductorlaser comes onto the market, the laser light required for functioning asa light source is emitted from the first semiconductor laser 201, sothat it is unnecessary to operate the second semiconductor laser 202.Therefore, electrode terminals disposed on the package are connectedonly to the first semiconductor laser 201. Alternatively, aconfiguration in which after the semiconductor laser is sold andattached to various electronic apparatuses, a current is caused to flowto the second semiconductor laser 202 at regular intervals or atirregular intervals so as to perform the gettering may be adopted.

In the case where the light source of this embodiment is used in anelectronic apparatus such as an optical disk apparatus, first, a biasvoltage is applied to the second semiconductor laser 202 for apredetermined period of time (for 24 hours, for example), so as toproduce laser oscillation. Accordingly, foreign materials containingcarbon and Si existing in the package are deposited on the emitting endfaces of the second semiconductor laser 202. In a preferred embodiment,such gettering is performed before the light source of this embodimentis attached to the optical disk apparatus or the like.

As the optical power of the second semiconductor laser 202 is increased,a higher effect of the gettering can be attained. Therefore, it ispreferred that the stripe width of the second semiconductor laser 202 beset to be larger, so as to increase the optical power. As describedabove, the stripe width of the second semiconductor laser 202 is set inview of the gettering effect, irrespective of the stripe width of thefirst semiconductor laser 201.

In this embodiment, one of the two end faces which constitute the cavityof the semiconductor laser on the side from which the laser light isemitted (a light emitting end face) is coated with an SiO₂ layer, andthe SiO₂ layer is further coated with TiO₂ layer. A backward end face asan end face on the opposite side to the light emitting end face iscoated with a multilayer film of SiO₂ and Nb₂O₅. The reflectivity of thelight emitting end face and the reflectivity of the backward end faceare set to be 10% and 90%, respectively. A power reflectivity of thelight emitting end face is adjusted in the range of 1% to 3% for thepurpose of increasing the optical power.

If the crystal structure of TiO₂ is appropriately selected, the TiO₂layer disposed on the light emitting end face exhibits photo-catalyticeffect, so as to decompose materials containing carbon. Therefore, thematerials which are to be subjected to the gettering are advantageouslyreduced.

In order to increase the photo-catalytic effect of TiO₂, it is preferredthat a layer of TiO₂ having an anatase-type crystal structure bedeposited on the light emitting end face of the semiconductor laser.However, there is no problem even if the anatase-type crystal structureand a rutile-type crystal structure mixedly exist. Such TiO₂ can bepreferably formed by sputtering such as RF sputtering or ECR sputtering,or by an application method by means of a TiO₂ sol spray, for example.

In this embodiment, when the TiO₂ layer positioned on the uppermostsurface of the light emitting end face of the semiconductor laser isirradiated with laser light, strong photo-catalysis occurs, so as tochange hydrocarbon existing in the periphery into CO₂, H₂O, and thelike. Accordingly, the deposition of carbon on the emitting end face ofthe semiconductor laser can be prevented.

When an oscillation wavelength of the laser is A, and the refractiveindex of the TiO₂ layer is n, it is preferred that the thickness of theTiO₂ layer deposited on the light emitting end face of the semiconductorlaser be substantially an integral multiple of λ/(2n).

In this embodiment, the semiconductor laser is fabricated by using then-type GaN substrate 101. However, the substrate is not necessarilyformed from GaN. The substrate for the semiconductor laser used in thepresent invention may be a substrate on which a III-V group nitridesystem semiconductor material can be epitaxially grown, such as asapphire substrate or an SiC substrate.

The semiconductor laser in this embodiment has two ridge stripestructures, but the number of ridge stripe structures may be 3 or more.In the case where the number of ridge stripe structures is N(N is aninteger of 2 or more), the number (M) of ridge stripe structures fordefining the semiconductor laser portion used for gettering satisfiesthe relationship of 1≦M≦N−1.

Even in a high power semiconductor laser which does not necessarilyrequire laser oscillation only in a fundamental transverse mode, if theconfiguration of the present invention is adopted, the deposition of theforeign materials on the light emitting end face of the firstsemiconductor laser 201 is suppressed.

Embodiment 2

Hereinafter, with reference to FIGS. 2A to 2C, a second embodiment of alight source according to the present invention will be described. Inthis embodiment, as a semiconductor light emitting device, a nitridesemiconductor laser is used.

The light source in this embodiment includes a semiconductor laser 301,a base 303 for mounting the semiconductor 301, and a cap 304, as shownin FIG. 2A. The fundamental configuration of the semiconductor laser 301used in this embodiment is similar to the configuration of thesemiconductor laser shown in FIG. 1, but the number of ridge stripestructure for current constriction can be one.

The cap 304 includes a transparent glass 306 for taking out the laserlight to the outside, and a can 305 for holding the glass 306. Thesemiconductor laser 301 is mounted on the base 303 via a sub mount 302,and hermetically sealed in a package constituted by the base 303, thecan 305, and the glass 306. Openings are disposed in the base 303 forpassing terminals therethrough, and the terminals are fixedly attachedby a low-melting glass 307. The terminals are connected to the terminalsof the semiconductor laser 301 by means of lines which are not shown.The glass 306 functions as a window for transmitting light (a lighttransmitting window).

In this embodiment, in order to increase the air-tightness, a gapbetween the glass 306 and the can 305 is bonded by means of alow-melting glass 308, as shown in FIG. 2B. On both of the uppermostsurfaces of the glass 306, TiO₂ layers 309 and 310 are formed.

When the TiO₂ layer 309 and the TiO₂ layer 310 coated on the uppermostsurfaces of the glass 306 are irradiated with light having wavelengthsof 450 nm or less, hydrocarbon existing on the periphery can be changedinto CO₂, H₂O, and the like by the photo-catalysis of TiO₂. Accordingly,the carbon is in a stable condition, so that the deposition of carbon onthe surface of the glass 306 can be prevented. At this time, materialscontaining Si are also decomposed, and rendered to be harmless.

In this embodiment, the TiO₂ layers 309 and 310 are not formed on theentire surface of the glass 306, but selectively formed on the outerside of the center portion of the glass 306. Therefore, if the foreignmaterials containing carbon or Si are deposited on the TiO₂ layers 309and 310, the deposition does not affect the transmission of needed laserlight emitted from the semiconductor laser 301. As a result, thereduction in optical intensity does not caused.

In order to increase the photo-catalytic effect, it is preferred thatthe temperatures of the TiO₂ layers 309 and 310 in light irradiation beincreased. Accordingly, in the TiO₂ layers 309 and 310, a region whichis especially desired to exhibit photocatalysis may be selectively dopedwith an ultraviolet absorbing material. Alternatively, as a lower layerand/or an upper layer of the TiO₂ layers 309 and 310, a layer includingan ultraviolet absorbing material may be formed. Preferably, such alayer including the ultraviolet absorbing material is not formed on theentire surface of the glass 306, but selectively formed on the outerside of the center portion of the glass 306. The layer including theultraviolet absorbing material may be formed from Si or GaAs, forexample.

As light with which the TiO₂ layers 309 and 310 are irradiated forcausing the photo-catalysis, light emitted from the semiconductor laser301 may be used. Alternatively, a light source may be disposed in thesealing package additionally to the semiconductor laser 301, and lightemitted from the light source may be used. Alternatively, in the casewhere light emitted from a light source which is disposed externally tothe sealing package may be incident on the TiO₂ layers, the same effectscan be attained. When the TiO₂ layers are irradiated with light emittedfrom other light sources, the TiO₂ layers may be formed not only on thesurface of the glass 306, but also on the surface of the cap 304 and/orthe base 303.

On the surface of the glass 306 in this embodiment, in order to increasethe taking-out efficiency of laser light, reflection free coating isperformed. When the oscillation wavelength of a laser chip is A and therefractive index of the TiO₂ layer is n, if the thickness of the TiO₂layers coated on the surface of the glass 306 is substantially anintegral multiple of λ/(2n), the reflectivity for obtaining high powerlaser can be easily and effectively controlled.

As shown in FIG. 2C, TiO₂ layers 311 and 312 may be deposited on thelow-melting glass 308 for adhering the glass 306 and the can 305. Withthis deposition, exhaustion of volatile components from the low-meltingglass 308 can be suppressed, and the density of the material to besubjected to gettering in the atmospheric gas can be reduced.

The semiconductor laser in this embodiment may have two or more ridgestripe structures. In addition, the semiconductor laser to be employedmay be a great power semiconductor laser which does not necessarilyrequire laser oscillation only in fundamental transverse mode.

Moreover, the light source of this embodiment uses the semiconductorlaser formed from the III-V group nitride semiconductor material. Thepresent invention is not limited to this. Alternatively, a lightemitting device such as a light emitting diode (wavelength of 450 nm orless, for example) may be used. The semiconductor material used for theproduction of such light emitting devices is not limited to the III-Vgroup nitride semiconductor material. The semiconductor material may beBAlGaInN, a mixed crystal compound semiconductor containing arsenic (As)and phosphorus (P), or other compound semiconductors.

Embodiment 3

Hereinafter, with reference to FIGS. 3A and 3B, a third embodiment of alight source according to the present invention will be described. Alsoin this embodiment, as a semiconductor light emitting device, a nitridesemiconductor laser element is used.

The light source of this embodiment includes a semiconductor laser 301,a base 303 for mounting the semiconductor laser 301, and a cap 304, asshown in FIG. 3A. The cap 304 includes a transparent glass 306 fortaking out laser light to the outside, and a can 305 for holding theglass 306. A main characteristic point of this embodiment resides inthat a gettering portion 401 for depositing a material containing carbongenerated from hydrocarbon or the like in the air or a materialcontaining Si is disposed in part of the base 303. The gettering portion401 is disposed in a position which does not interrupt the use of thesemiconductor laser.

Hereinafter, a fabrication method of the light source of this embodimentwill be described.

First, after the semiconductor laser 301 is mounted on the base 303together with a sub mount 302, the cap 304 is fused and attached ontothe base 303, and the semiconductor laser 301 is hermetically sealed bythe base 303 and the cap 304. Thereafter, as shown in FIG. 3B, in orderto perform the gettering of hydrocarbon and Si containing materialsexisting in the sealed inside, light (preferably having a wavelength of450 nm or less) from the outside is converged on the gettering portion401, thereby depositing materials containing carbon and Si. In theexample shown in the figure, ultraviolet rays emitted from an Hg lamp402 are converged on the gettering portion 401 by means of a condenser403.

The light source which is preferably used for the gettering methodincludes, other than the Hg lamp, a blue LED, a blue laser, anultraviolet LED, an ultraviolet laser, and the like.

In this embodiment, as the gettering portion 401, part of the base isutilized. However, the position in which the gettering portion 401 isformed may be in a region which does not interrupt the use of thesemiconductor laser 301. For example, the gettering portion 401 may bedisposed in a region other than the light emitting region of thesemiconductor laser, in a sub mount on which the laser chip is mounted,or in part of the cap (in an edge portion of the glass, or the like).

In order to further increase the gettering effect, it is preferred thatthe temperature of the gettering portion 401 be increased in gettering.If a material which generates heat by absorbing ultraviolet rays isdisposed in the gettering portion, the temperature of the getteringportion 401 can be increased without using additional heating means.

Embodiment 4

With reference to FIGS. 4A and 4B, an embodiment of the optical pickupapparatus of the present invention will be described.

FIG. 4A is a perspective view showing an optical unit used in thisembodiment. The optical unit has a construction in which a semiconductorlaser and a photo detector are integrated. FIG. 4B shows a constructionof an optical pickup including the optical unit as a component.

The optical unit includes a semiconductor laser 501 for emitting laserlight having a wavelength of 450 nm or less, an optical system forconverging laser light emitted from the semiconductor laser 501 on arecording medium, and a photo IC (a photo detector) 502 for detectinglaser light reflected from the recording medium.

As shown in FIG. 4A, a recessed portion is formed in the center of aprincipal surface of an Si substrate 503 (7 mm×3.5 mm), and thesemiconductor laser 501 is disposed on a bottom face of the recessedportion. One side face of the recessed portion formed in the principalsurface of the Si substrate 503 is inclined, and functions as a micromirror.

In the case where the principal surface of the Si substrate 503 is a(100)-orientated plane, a (111) plane is exposed by anisotropic etching,and the (111) plane can be utilized as a micro mirror. The (111) planeforms an angle of about 54 degrees with respect to the (100) plane. Forthis reason, if an offset substrate in which the principal surface isinclined by about 9 degrees from the (100) plane is used, the (111)plane which is inclined by 45 degrees from the principal surface can beobtained. A (111) plane disposed in a position opposed to the (111)plane forms an angle of 63 degrees with respect to the principalsurface, but a micro mirror is not formed on the plane. On the plane, aphoto diode for monitoring optical power is formed.

The (111) plane formed by the anisotropic etching is a smooth mirrorface, so that the plane functions as a superior micro mirror. In orderto further increase the reflectivity of the micro mirror, it ispreferred that at least a portion functioning as the micro mirror of theinclined face of the Si substrate 503 be covered with a metal film.

On the Si substrate 503, other than the photo diode for monitoring theoptical power of the semiconductor laser 501, a photo diode and a photoIC 502 for detecting an optical signal constituted by a signalprocessing circuit are formed.

The above-described optical unit is preferably used in a condition wherethe optical unit is hermetically sealed in a resin lead frame package504 by a glass cap 506, as shown in FIG. 4B.

Hereinafter, with reference to FIG. 4B, the optical pickup apparatus ofthis embodiment will be described.

Laser light emitted from the semiconductor laser 501 in the optical unitis reflected by the micro mirror, and propagates in a directionsubstantially perpendicular to the principal surface. The laser lightpassing through the glass cap 506 is separated into three light beams bygrating formed on a polarizing hologram element 507. For simplicity, inFIG. 4B, only one light beam is shown.

Thereafter, the light beams separated by the polarizing hologram element507 transmit through a quarter-wave plate (not shown) and an objectivelens 508, and then the light beams are converged on an optical disk 509.

The laser beams reflected from the optical disk 509 transmit through theobjective lens 508 and the quarter-wave plate (not shown), and then thelaser beams are diffracted by the grating formed on an upper face of thepolarizing hologram element 507. The diffracted light is incident on thephoto IC 502 in the optical unit, thereby generating an informationsignal, a focus error signal, and a tracking error signal.

As described above, if the unit in which the semiconductor laser isintegrated with the photo detector such as the photo diode and the photoIC is used, the electronic ap-paratus such as the optical disk apparatuscan be miniaturized.

According to such an optical unit, the positional relationship betweenthe semi-conductor laser and the photo detector is previously fixed inappropriate positions, so that optical alignment can be easilyperformed, assembly accuracy is high, and the fabrication process iseasily performed.

In this embodiment, a gettering portion 505 for depositing a compoundcontaining carbon generated from hydrocarbon and the like in the air isdisposed in part of the Si substrate 503. The gettering portion 505 hasthe same configuration as that of the gettering portion 401 in theabove-described embodiment. The position in which the gettering portion505 is formed is determined so that the operations for data writing tothe optical disk 509 and data reading from the optical disk 509 are notinterrupted. Specifically, the gettering portion 505 is disposed in aregion which does not cross the light path of laser light emitted fromthe semiconductor laser 501 and the light path of laser light reflectedand returned from the optical disk 509.

Next, a fabrication method of the optical unit in this embodiment willbe described.

First, an optical unit in which a semiconductor laser 501 and a photo IC502 are integrated is mounted on a resin lead frame package 504. Then, aglass cap 506 is attached to the resin lead frame package 504 in an N₂gas atmosphere, thereby hermetically sealing the optical unit in thepackage 504.

In this embodiment, the glass cap 506 is attached to the resin leadframe package 504 via an adhesive. As the adhesive, an epoxy resin orthe like may be used, for example.

The N₂ gas is enclosed in the package, so that the inside of the packageis in a clean gas atmosphere. However, a slight amount of organic(containing carbon) may sometimes scatter from the epoxy resin. In thisembodiment, in order to catch the carbon or a slight amount of Sicontaining materials included in the air, light from the outside isconverged on a gettering portion 505, so as to deposit the materialscontaining C and/or Si on the gettering portion 505.

A light source used for the gettering is a light source for emittinglight having a wavelength of 450 nm or less, preferably a light sourcefor emitting light having a wavelength of 400 nm or less. Light sourceswhich are preferably used include an Hg lamp, a blue LED, a blue laser,an ultraviolet LED, an ultraviolet laser, and the like. Among such lightsources, if a light source can be miniaturized, the light source can bedisposed in the inside of the package.

In this embodiment, the semiconductor laser, the photo detector, and themicro mirror are fixed on one and the same substrate, but the elementsmay be separately disposed.

Embodiment 5

With reference to FIG. 5, an embodiment of the optical disk apparatusaccording to the present invention will be described. The optical diskapparatus of this embodiment includes an optical pickup apparatus whichis shown. The components other than the optical pickup apparatus arefundamentally the same as those in a known optical disk apparatus.Therefore, hereinafter, the configuration of the optical pickupapparatus will be described.

The optical pickup apparatus shown in the figure includes a light source601 for emitting laser light having a wavelength of 408 nm, a collimatorlens 602 for collimating laser light emitted from the light source 601,a diffraction grating (not shown) for separating the collimated lightinto three light beams, a half prism 603 for transmitting and/orreflecting a specific component of the laser light, and a condenser 604for converging the laser light from the half prism 603 on an opticaldisk 605. On the optical disk 605, a spot of converged laser is formed,thereby reading information (data) which is recorded on the op-ticaldisk 605, or writing user data to the optical disk 605.

After the laser light reflected from the optical disk 605 is reflectedby the half prism 603, the laser light transmits through aphoto-receiving lens 606, and then enters into a photo IC 607. The photoIC 607 includes a photo diode which is divided into a plurality ofportions. Based on the laser light reflected from the optical disk 605,the photo IC 607 generates an information reproduction signal, atracking signal, and a focus error signal. By the tracking signal andthe focus error signal, a driving system such as an actuator moves anoptical system including a lens, so that a position of the laser spot onthe optical disk 605 is adjusted.

As described above, the optical disk apparatus in this embodiment isprovided with the optical pickup apparatus including the light source601, the converging optical system for converging laser light emittedfrom the light source 601 onto a recording medium, and the photodetector (the photo IC 607) for detecting laser light reflected from therecording medium, and also provided with an apparatus for generatingplasma (a plasma cleaning apparatus 608) in the vicinity of the opticalpickup apparatus.

The plasma cleaning apparatus 608 generates ion or ozone from oxygen andmoisture in the air. The ion or ozone generated by the plasma cleaningapparatus 608 changes hydrocarbon into CO₂, H₂O, and the like byoxidation. Thus, the deposition of carbon on the surface of thecomponents (the semiconductor laser, the lens, the mirror, and the like)of the optical pickup portion is prevented. In addition, carbon adheringto the components can be decomposed into CO₂ or the like, and removed.The ozone has an additional effect of decomposing an Si containingmaterial such as siloxane.

Since the plasma cleaning apparatus 608 functions as an apparatus forperforming gettering, decomposition, or vaporization of a foreignmaterial which tends to adhere to the surface of the element, it isunnecessary for the plasma cleaning apparatus to always operate. Forexample, the plasma cleaning apparatus 608 may be operated atpredetermined intervals, or when a reduction in optical intensity oflight emitted from the semiconductor laser is observed, therebyperforming the cleaning.

As the light source 601, it is preferred that the light source in theabove-described embodiment be used.

Embodiment 6

With reference to FIG. 6, another embodiment of the optical diskapparatus according to the present invention will be described. Theoptical disk apparatus of this embodiment has an optical pickupapparatus shown in the figure. The components other than the opticalpickup apparatus are fundamentally the same as those in a known opticaldisk apparatus.

The optical disk apparatus of this embodiment includes an optical pickupwhich is the same as that in the optical pickup apparatus shown in FIG.5, and also includes a TiO₂ plate 609 and an Hg lamp 610 disposed in thevicinity of the optical pickup apparatus.

The TiO₂ plate 609 is a member of which the surface is coated with theabove-described TiO₂ layer. The Hg lamp 610 is a light source foremitting light having a wavelength of 450 nm or less, and morepreferably 400 nm or less to the TiO₂ plate 609.

When the TiO₂ plate 609 is irradiated with the light emitted from the Hglamp 610, hydrocarbon in the atmospheric gas is decomposed and changedinto CO₂, H₂O, or the like, by strong photo-catalysis of TiO₂. Thus, thedeposition of carbon on the surface of the components (the semiconductorlaser, the lens, the mirror, and the like) of the optical pickup portionis prevented.

The lightening of the Hg lamp 610 as the light source for causing thephotocatalysis is not always performed, but may be performed atpredetermined intervals, or when a reduction in optical intensity oflight emitted from the semiconductor laser is observed,

The TiO₂ plate 609 is disposed in the vicinity of the optical pickupportion. Alternatively, the optical pickup portion or the optical disksystem may be covered with a plate to which TiO₂ adheres.

Instead of the additional provision of the plate 609 to which TiO₂adheres, such a configuration may be alternatively adopted that theuppermost surface of the lens, the prism, and the like which constitutethe optical pickup portion is coated with TiO₂, and the portion may beirradiated with light.

When the surface of the components of the optical pickup portion iscoated with TiO₂, the thickness of the TiO₂ layer is set to be a valuewhich does not deteriorate the functions of the respective components.When the oscillation wavelength of laser is A, and the refractive indexof TiO₂ is n, it is preferred that the thickness of the TiO₂ layer besubstantially an integral multiple of λ/(2n).

If the semiconductor laser in Embodiments 1 to 6 is used as the lightsource 601, an optical disk apparatus with high reliability which stablyoperates for the long term can be obtained.

In the above-described respective embodiments, the semiconductor laseris fabricated by using the n-type GaN substrate, but it is not necessarythat the substrate be formed from GaN. The substrate of thesemiconductor laser used in the present invention may be a substrate onwhich a III-V group nitride semiconductor material can be epitaxiallygrown, such as a sapphire substrate or SiC substrate.

The light emitting device used in the above-described respectiveembodiments is a semiconductor laser formed from a III-V group nitridesemiconductor material, but the present invention is not limited tothis. The light emitting device may be a light emitting device such as alight emitting diode (especially having a wavelength of 450 nm or less).The semiconductor material used for the fabrication of such a lightemitting device is not limited to the III-V group nitride semiconductormaterial. If the semiconductor material can emit light, thesemiconductor material may be BAlGaInN, or a mixed crystal compoundsemiconductor containing arsenic (As) and phosphorus (P).

Embodiment 7

Next, with reference to FIG. 9, a laser projection type display will bedescribed as an embodiment of an apparatus provided with the lightsource of the invention.

The laser projection type display includes blue, green, and red laserlight sources 900 a, 900 b, and 900 c, a spatial modulating element 902,and a projection lens 904. Image information is projected on a screen906. The blue, green, and red laser light sources 900 a, 900 b, and 900c are light sources described in the embodiments of the presentinvention, and have the construction shown in FIG. 1, for example.

Laser light beams emitted from the laser light sources 900 a, 900 b, and900 c are coherent, so that a speckle noise is caused in the imageformed on the screen 906. In order to remove the speckle noise, it ispreferred that a scattering plate (not shown) or the like is inserted onan optical path, so as to cause vibration. Instead of the spatialmodulating element 902, a two-dimensional scanning optical systemincluding a mirror or the like may be used.

The most important techniques for practically use the laser projectiontype display are the performance, the lifetime, and the reliability ofthe blue, green, and red lasers 900 a, 900 b, and 900 c. The red laserlight is produced by using an AlGaInP semiconductor material, andobtained by a high-power semiconductor laser with high reliability.However, high-power semiconductor lasers with high reliability whichemit blue and green laser light are not yet realized.

As the semiconductor laser for emitting laser light having a wavelengthrange of blue or green, a nitride semiconductor laser is promising. Forexample, in a light emitting layer of a blue-violet laser, InGaNsemiconductor is used. If a mole ratio of In in the InGaN semiconductoris increased, it is possible to increase a laser oscillation wavelength.

In the case of the semiconductor laser of a region of blue or green, ascompared with the semiconductor lasers of blue-violet, violet, andultraviolet, a reduced amount of foreign material adheres to the lightemitting end face. However, visible laser used in a laser display ishigher power than the laser used in an optical disk. For this reason,the adhesion of foreign materials to the light emitting end face or thelike results in a problem.

In this embodiment, the above-mentioned material containing carbon orsilicon is removed by gettering or decomposed by plasma, so that alarge-screen laser projection type display with high luminance can berealized.

Since the laser display is an electronic apparatus using high-powerlaser, the adhesion of a material containing carbon or silicon to theelements included in the optical system in such an electronic apparatus(a lens, a spatial modulating element, or the like) may cause a problem.However, as in the above-described embodiments, an apparatus forperforming gettering, decomposition, or vaporization of a foreignmaterial which tends to adhere to the surface of the component isdisposed, so that the adhesion to the optical system can be reduced.Thus, stable operation can be realized.

As described above, according to the present invention, by the functionof the gettering portion or the gettering apparatus, gettering ordecomposition of materials mainly containing carbon or silicon isperformed, so that it is possible to provide a light source which canstably operate for the long term, and various apparatuses provided withthe light source.

The light source of the present invention is useful as a light sourcefor reading and writing data in optical disk related fields. Moreover,the light source of the invention can be applied to various electronicapparatuses such as a laser printer, and a laser display.

While the present invention has been described in a preferredembodiment, it will be apparent to those skilled in the art that thedisclosed invention may be modified in numerous ways and may assume manyembodiments other than that specifically set out and described above.Accordingly, it is intended by the appended claims to cover allmodifications of the invention which fall within the true spirit andscope of the invention.

1. A light source comprising: a semiconductor light emitting devicewhich has a light emitting face and emits light from part of the lightemitting face; a container which has a light transmitting window fortransmitting the light and accommodates the semiconductor light emittingdevice; and a gettering portion for performing gettering of a materialcontaining at least one of carbon and silicon, wherein the getteringportion is positioned, in the container, in a region other than the partof the light emitting face of the semiconductor light emitting device.2. The light source of claim 1, wherein a TiO2 layer is formed in partof a region which is irradiated with the light in the container.
 3. Thelight source of claim 2, wherein, when an oscillation wavelength of thesemiconductor light emitting device is λ, and a refractive index of theTiO2 layer is n, a thickness of the TiO2 layer is substantially anintegral multiple of λ/(2n).
 4. The light source of claim 1, wherein thesemiconductor light emitting device includes: a substrate; a multilayerstructure including a first conductive-type cladding layer, an activelayer, and a second conductive-type cladding layer, the multilayerstructure being formed on the substrate; a main current confinementstructure for injecting a carrier into a first region of the activelayer; and a sub current confinement structure for injecting a carrierinto a second region of the active layer, and a portion of the lightemitting face from which light generated in the second region of theactive layer is emitted functions as the gettering portion.
 5. The lightsource of claim 1, wherein the container includes: a supporting memberon which the semiconductor light emitting device is placed; and a cap towhich the light transmitting window is fixedly attached, the capcovering the semiconductor light emitting device, and the getteringportion is positioned on the supporting member.
 6. The light source ofclaim 1, wherein the container includes: a supporting member on whichthe semiconductor light emitting device is placed; and a cap to whichthe light transmitting window is fixedly attached, the cap covering thesemiconductor light emitting device, and the gettering portion ispositioned in a region of an inner face of the light transmitting windowwhich is not irradiated with the light.
 7. The light source of claim 1,wherein the semiconductor light emitting device is formed from a III-Vgroup nitride semiconductor material.
 8. An optical unit comprising: asemiconductor light emitting device which has a light emitting face andemits light from part of the light emitting face; a photo-detectionelement; a container which has a light transmitting window fortransmitting the light and accommodates the semiconductor light emittingdevice and the photo-detection element; and a gettering portion whichperforms gettering of a material containing at least one of carbon andsilicon, wherein the gettering portion is positioned in a region of thelight emitting face other than the part of the light emitting face ofthe semiconductor light emitting device in the inside of the container.9. The optical unit of claim 8, wherein a wavelength of the light is 450nm or less.
 10. An optical pickup apparatus comprising: a semiconductorlight emitting device which has a light emitting face and emits lightfrom part of the light emitting face; an optical system for convergingthe light emitted from the semiconductor light emitting device onto arecording medium; a photo detector for detecting light reflected fromthe recording medium; and a gettering portion for performing getteringof a material containing at least one of carbon and silicon, wherein thegettering portion is positioned in a region of the light emitting faceother than the part of the light emitting face of the semiconductorlight emitting device.
 11. The optical pickup apparatus of claim 10,wherein a wavelength of the light is 450 nm or less.
 12. The opticalpickup apparatus of claim 11, further comprising: a semiconductorsubstrate for supporting the semiconductor light emitting device,wherein the photo detector includes a plurality of photo diodes formedon the semiconductor substrate.
 13. The optical pickup apparatus ofclaim 11, wherein the semiconductor substrate is formed from silicon,the semiconductor substrate has a recessed portion formed on a principalsurface and a micro mirror formed on one side face of the recessedportion, the semiconductor light emitting device is disposed in therecessed portion of the silicon substrate, and an angle formed by themicro mirror and the principal surface of the semiconductor lightemitting device is set so that the light emitted from the semiconductorlight emitting device propagates in a direction substantiallyperpendicular to the principal surface by means of the micro mirror. 14.The optical pickup apparatus of claim 11, wherein the semiconductorlight emitting device is formed from a III-V group nitride semiconductormaterial.
 15. An electronic apparatus comprising: a semiconductor lightemitting device which has a light emitting face and emits light frompart of the light emitting face; and an apparatus for performinggettering, decomposition, or vaporization of a material containing atleast one of carbon and silicon.
 16. The electronic apparatus of claim15, wherein the apparatus includes a light source which emits lighthaving a wavelength of 450 nm or less.
 17. The electronic apparatus ofclaim 16, wherein the electronic apparatus further comprises a photocatalytic effect material film disposed in a position which receives atleast part of the light emitted from the light source, wherein the photocatalytic effect material film has a function of decomposing andvaporizing a compound of carbon or Si.
 18. The electronic apparatus ofclaim 16, wherein the light source is an Hg lamp, a blue LED, a bluelaser, an ultraviolet LED, or an ultraviolet laser.
 19. The electronicapparatus of claim 15, wherein the apparatus is an apparatus forgenerating plasma.
 20. The electronic apparatus of claim 15, wherein thesemiconductor light emitting device is formed from a III-V group nitridesemiconductor material.